A brake system typically includes a brake caliper that supports at least one brake piston. The brake piston is adapted to move at least one brake pad into contact with a moving component to create a clamping force. The clamping force may be adapted to slow, stop, or prevent movement of the moving component. In vehicular applications, the moving component may be a brake rotor that is in communication with a road wheel.
Some brake systems are operable in two applications, namely a hydraulic application, and an electromechanical application. The hydraulic application may be used to apply and/or release a service brake, and the electromechanical application may be used to apply and/or release a parking brake, or vice versa.
During the hydraulic application, a fluid may be pressurized, which may cause the brake piston to move into contact with the brake pad, and then move the brake pad into contact with the moving component to create the clamping force. Depressurizing the fluid may cause the brake piston to move away from the brake pad and then the brake pad to move out of contact with the moving component to release the clamping force.
During the electromechanical application, torque from a motor may be converted into a linear force by way of a rotary to linear stage mechanism. The linear force may be adapted to move the brake piston into contact with the brake pad, and then move the brake pad into contact with the moving component to create the clamping force.
A typical rotary to linear stage mechanism comprises a spindle and a nut. The spindle is in rotational communication with the motor, and the nut is threadably connected to the spindle. The nut is received in a piston pocket of the brake piston. Rotation of the spindle causes the nut to move axially along a length of the spindle and eventually into contact with a bottom wall of the piston pocket. With the nut in contact with the bottom wall of the piston pocket, continued movement of the nut causes the nut to push the brake piston into contact with the brake pad and then move the brake pad into contact with the moving component to create the clamping force.
A gap is typically defined between the nut and the bottom wall of the piston pocket. Thus, during the electromechanical application, the nut must first be moved to take up or eliminate the gap before movement of the nut actually pushes or moves the brake piston.
During the hydraulic application, an axial starting and stopping position of the brake piston changes over time. Stated another way, over time the brake piston is moved further out of the piston pocket in a direction closer towards the brake rotor as a result of brake pad wear. However, an axial position of the nut relative to the brake piston typically does not change during the hydraulic application. As can be imagined, over time, especially if the electromechanical application is used infrequently, the gap increases between the bottom wall of the brake piston and the nut. The size or magnitude of the gap may correspondingly increase the response time of the electromechanical application because the gap must first be taken up or eliminated before movement of the nut causes the brake piston thus the brake pad to move into contact with the moving component to create the clamping force.
It may therefore be desirable to have a brake system where an axial position of the nut changes together with an axial position of the brake piston during the hydraulic application. Stated another way, it may be desirable for the nut to be moved axially with the brake piston during the hydraulic application so that the gap between the nut and the bottom pocket wall remains substantially the same over time. This may advantageously reduce the lag time between the initial time when the electromechanical application is activated to when the nut makes contact with the brake piston and causes the brake piston to move the brake pad against the moving component to create the clamping force.